There is a semiconductor device which has a transistor such as a power metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT) in which a gate insulating film is formed on an inner wall of a trench formed in a front surface of a semiconductor substrate.
US 2015/0021623 discloses a MOSFET in which a gate insulating film including an oxide film, a nitride film, or a laminate structure of the oxide film and the nitride film is formed on an inner wall of a trench.
JP-A 2001-210821 discloses a transistor in which a gate insulating film having a laminate structure of an oxide film, a nitride film, and an oxide film is formed on a bottom of a trench and a gate insulating film including an oxide film is formed on sidewalls of the trench.